Low-temperature Sintering of Zinc Oxide Varistors
Carter, C. B.
High-field varistors in the system ZnO-CoO-MnO-Bi2O3 were fabricated using powders prepared by a previously developed coprecipitation process. Following calcination, the powders were compacted and densified by conventional pressureless sintering at temperatures below 750° C in air, The effects of sample green density, sintering temperature, and grain-growth inhibitor on densification and microstructure development were investigated. Addition of aluminium at the 125 p.p.m level was used to inhibit grain growth. Samples with densities >0.98 theoretical and grain sizes <1μm were fabricated by high-pressure cold-isostatic pressing followed by sintering at 730° C. For comparison, typical commercial varistor devices have grain sizes of about 20 μm and switching fields of approximately 2 kV cm−1 after sintering at 1200 to 1400° C. As a result of the fine grain size, our high-field varistors had switching fields of 45 kV cm−1 at a current density of 10 A cm−2. Consistent with earlier work on extremely high-density varistors (>0.98 theoretical) prepared from similar powders, nonlinearity coefficients of about 10 were measured for current densities between 2.5 and 10 A cm−2.
M. N. Rahaman et al., "Low-temperature Sintering of Zinc Oxide Varistors," Journal of Materials Science, Springer Verlag, Jan 1990.
The definitive version is available at http://dx.doi.org/10.1007/BF00714102
Materials Science and Engineering
Keywords and Phrases
Polymer Sciences; Industrial Chemistry/Chemical Engineering; Characterization and Evaluation Materials; Mechanics
Article - Journal
© 1990 Springer Verlag, All rights reserved.